Wire cut or die sinker EDM: choosing the right process
An EDM machine removes metal with electrical discharges instead of a cutting edge, so the hardness of the workpiece stops being a limit. Only one property matters, the material has to conduct electricity. Two machine types share the work.
- Die sinker EDM machines sink a shaped electrode into the workpiece and leave a closed form behind: cavities, pockets, internal contours and square internal corners.
- Wire cut EDM machines pass a thin wire through the workpiece and cut a profile all the way through, which suits dies, cutting plates and tight radii.
If the feature is closed at the bottom, it belongs on a die sinker. If the cut goes right through, it belongs on a wire machine.
EDM machines in South African industry
Tool, die and mould shops are the core users. Typical work covers injection and die casting moulds, forging dies, press tools, cutting plates and punches. In South Africa the pull often comes from further afield. Mining and mineral processing, oil and gas, heavy engineering and rail need hardened components repaired or replaced quickly, and those parts are frequently too hard or too detailed for conventional machining. Releasing a broken tap or drill from a large casting is another routine job that saves a component from the scrap bin.
Which materials can be cut on an EDM machine
Electrical conductivity is the only requirement. That brings in the materials that cause the most trouble elsewhere: hardened tool steel, tungsten carbide, titanium, Inconel and other nickel based alloys, stainless steel, copper alloys and aluminium, plus conductive ceramics and graphite. Since no mechanical force is applied, a tool can be hardened first and finished to size afterwards. Materials that do not conduct, plastics and glass among them, cannot be processed this way.
Electrodes for die sinker EDM
On a die sinker the electrode does the shaping, so its material matters as much as the machine. Two choices dominate:
- Graphite gives high removal rates and is quick to machine, which suits large areas and roughing.
- Copper and copper alloys resist wear on fine detail and leave a finer surface, which suits finishing.
Most shops use both, roughing with graphite and finishing with copper. Several electrodes per cavity are normal, so electrode consumption belongs in the costing from the beginning. The electrodes themselves are usually machined on a CNC milling machine.
Numerical control, accuracy and surface quality
Every EDM machine is numerically controlled, there is no conventional version of this machine type. The control regulates feed, discharge energy and flushing and keeps the spark gap constant. The gap between electrode and workpiece measures a few hundredths of a millimetre and is programmed in as an allowance so the part finishes on size. Higher discharge energy removes material faster and leaves a coarser surface, a fine finishing cut takes longer and produces the required quality. Accuracy rather than speed is what this process sells.
Dielectric, EDM wire and consumables
The process takes place in a dielectric fluid that insulates, cools and flushes eroded particles out of the gap. An oil based dielectric is normal on a die sinker, while wire machines run on deionised water. The ongoing requirements are EDM wire, filters, ion exchange resin and guides, all listed under EDM consumables. Consumables and filter changes are part of the running cost and should be planned before the machine is installed, particularly where import lead times apply.
Why KNUTH in South Africa
KNUTH has supplied machine tools since 1923 and carries both processes, with the focus on entry level and mid range machines rather than the high end. That is the segment most South African tool rooms actually buy in, where price and capability have to meet. We do not build the machines ourselves: we select the series, test them in Germany against a documented checklist and support them afterwards. The regional base in Germiston near Johannesburg serves South Africa and Sub-Saharan Africa, together with local service partners. Every machine is inspected to European testing standards with documented results, and the documentation is provided on request. Tell us what you machine and we will tell you which EDM machine type fits alongside the milling machines and grinding machines you already run.
Service, spare parts and availability
Service is handled from the regional base together with local service partners. Common spare parts are supplied from stock, special parts come directly from the manufacturers of the components. The company wide spare parts supply commitment runs for ten years. Service enquiries reach the service planning team by email or telephone and receive a reply on any working day. Installation, commissioning and operator training can be arranged on request, with the scope set out in the quotation. Prices depend on the process, the working area and the equipment level, so every machine is quoted individually. Contact us by email or phone for a quotation, for delivery times or if you are deciding between wire cutting and die sinking.
Further Machine Categories at a Glance
Here is an overview of our machine range. Select a category to learn more about individual machines and their technical data.
